feat(06-01): create GitHub Actions test workflow

- Tests workflow: push/PR to main + workflow_dispatch
- 3x3 matrix: ubuntu/macos/windows x Node 18/20/22 (9 jobs)
- Concurrency groups with cancel-in-progress
- 10-minute timeout, fail-fast enabled
- Steps: checkout, setup-node with npm cache, npm ci, npm test

.github/workflows/test.yml

@@ -0,0 +1,40 @@
+name: Tests
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 10
+
+    strategy:
+      fail-fast: true
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        node-version: [18, 20, 22]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run tests
+        run: npm test